Mairsil, the Pretender + Blood Vassal + Endling + Spike Feeder

Mairsil, the Pretender

Blood Vassal

Endling

Spike Feeder

How it works

1. Activate Mairsil using Endling's third ability by paying , giving Mairsil undying until end of turn.
2. Activate Mairsil using Blood Vassal's ability by sacrificing it, adding .
3. Mairsil dies, triggering its undying ability, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
4. Activate Mairsil using Spike Feeder's second ability by removing a +1/+1 counter from it, causing you to gain 2 life.
5. Repeat.

This loop turns Mairsil, the Pretender into a self-sustaining engine by letting her feast upon the abilities of her caged subjects. By utilizing Endling's caged undying ability, Mairsil is able to shrug off her own sacrifice to Blood Vassal's mana-generating ability, returning to the battlefield with a +1/+1 counter ready to fuel Spike Feeder's life-gaining removal. Because Mairsil resets herself upon death, this cycle can be repeated indefinitely to yield infinite black mana, infinite life, and an endless stream of enters-the-battlefield and death triggers.